The structure and harmonic vibrational frequencies have been determined for the alkaline-earth metal MNO2 systems (M = Be, Mg, Ca, and Sr) using the B3LYP method. Binding energies have also been calculated using conventional ab initio methods, CCSD(T), and MCPF, with different basis sets. Four different coordination modes of NO2 to the metal have been considered. The C-2 upsilon eta(2)-O,O coordination mode is the most stable one for all metals. However, for BeNO2 the ground state is a B-2(1) state while for the other metals the (2)A(1) state is the most stable one. Our best estimates for the D-0 binding energies are 77 kcal mol(-1) for BeNO2, 53 kcal mol(-1) for MgNO2, 69 kcal mol(-1) for CaNO2, and 71 kcal mol(-1) for SrNO2.